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Space Suit and Extravehicular Activities

Space Suit's Functions and Capabilities
Mission specialist Doi performing EVA in November 1997
General view of space suit for space shuttle
Space Suit Main Components
A "space suit" is a system that enables man to leave a spacecraft and conduct extravehicular activities (EVA) in space.
Until now, space suits have been developed in the United States and in the former Soviet Union (Russia) to broaden man's activities in space. From the days of the Apollo mission activities on the Moon to the capture of a satellite by Astronaut Doi in November 1997 and the construction of the International Space Station (ISS) that began in November 1998, the space suit has been an essential element of man's activities in space.
The three basic functions of the space suit are:

1. Maintain an appropriate pressure for the human body in space.
2. Provide oxygen necessary for life, remove carbon dioxide, and control the temperature and humidity.
3. Enable man to perform necessary work in space.

Pressure suits worn by pilots of high-altitude aircraft could be improved for use in space. For this reason, space suits were originally based on such pressure suits and developed in the United States through experience in Mercury, Gemini, Apollo, and the space shuttle program. At present, space suit systems used aboard the space shuttle are composed of the space suit itself and the life-support system.

The space suit has functions to maintain the pressure (0.3 atmospheres) and to provide mobility, thermal protection, cooling, sunlight protection, and micrometeorite protection. It is composed of the hard upper torso, lower torso assembly, arm assembly, gloves, helmet/extravehicular visor assembly, and liquid cooling and ventilation garment.

The life-support system supplies oxygen for breathing, removes carbon dioxide, controls the pressure and temperature in the space suit, supplies the water for the water-cooled underwear, and maintains communication with the space shuttle. The space suit is composed of the primary life-support system, the secondary oxygen pack, and control panel.

The combined space suit and life support system weigh a total of 125 kilograms and can support a seven-hour EVA. Figure 4 shows the main components of the space suit. impose burdens on the astronauts performing microgravity experiments and that a human-friendly design had been achieved.

This experiment was conducted through the cooperation of numerous organizations. These included, NASDA, Ishikawajima-Harima Heavy Industries, the University of California, NASA Ames Research Center, and NASA Johnson Space Center. Looking towards the future era of international cooperation, this experiment in which Japanese and American researchers and engineers combined their efforts and worked together was a truly valuable experience.

Necessary EVA Preparations
To conduct an actual EVA such as for constructing the ISS, the following detailed preparations are needed.
Hardware Verification
Test Scene in Weightless Environment Test Facility
The EVA hardware must be designed so that an astronaut in space can perform his or her work easily. For example, it must be designed so that the astronaut can transfer easily to the workplace and each EVA tool must be placed where it is easily accessible. Furthermore, the hardware should be designed so that astronauts can fix their positions, which will enable them to easily distinguish the objects they are working with. Before this hardware is actually used in space, verification tests are conducted on the ground to ensure this hardware meets the above requirements.

These verification tests are conducted underwater in a large pool (weightless environment simulation tank) to simulate microgravity conditions. This underwater test is called the "weightless environment simulation test." In this test, buoyancy in water and the force of gravity are balanced to create a neutral buoyancy condition in which objects neither float nor sink. The pool contains a full-scale mockup of the hardware. Astronauts wearing a test suit (almost same as the space suit) enter the pool and perform the activities to ensure that they can actually be done in space.

Tests have been conducted with an underwater, full-scale mockup of the Japanese Kibo module at Tsukuba Space Center's Weightless Environment Test Facility.

Preparations by Astronauts
In the space shuttle mission, basic EVA training necessary for shuttle operations is conducted in the mission specialist training course. EVA training includes confirming the fit of the space suit for each astronaut, utilization of basic EVA tools, and practice in using the pool for space environment simulation test. When an EVA is planned in space shuttle missions, the mission specialists are assigned and the details and procedures of the EVA operations are decided. The procedures are rehearsed to determine if they can be accomplished within the decided time and if the mission specialists can properly respond to any problems that might occur. Based on this training, the procedures can then be modified as necessary. The weightless environment simulation tank is often used in this training.

Special Preparation time for Actual EVA
For an actual EVA, over ten hours of special preparation is needed before the mission specialists don the space suit and exit the spacecraft. This time is necessary for the mission specialists to adjust from the one atmosphere cabin pressure (oxygen 21%, nitrogen 79%) to the space suit environment (0.3 atmospheres, pure oxygen).

If humans are subjected to such changes in a short period, they may suffer from decompression sickness. To avoid this, the mission specialists breathe pure oxygen for a certain time period before the atmospheric pressure is reduced. This is called prebreathing and reduces the nitrogen in the mission specialists' bodies.

In practice, over 12 hours before the EVA, mission specialists perform prebreathing for 60 minutes in one atmosphere pressure. Just before the end of the prebreathing period, the cabin pressure is reduced to 0.7 atmospheres (27% oxygen, 73% nitrogen) and held at that pressure for over 12 hours. After that, the mission specialists don the space suit and perform final prebreathing for 40 to 75 minutes, then exit the spacecraft and perform the EVA.

ISS, which is to be assembled by 2004, requires many EVAs to be planned. EVA techniques will thus become more and more important for manned space activities from now on.

Last Updated : March 2,1999

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